Steering control for industrial truck with hydraulic wheel drive motors



Dec. 18, 1956 w. FERRIS STEERING CONTROL FOR INDUSTRIAL TRUCK WITHHYDRAULIC WHEEL DRIVE MOTORS 3 Sheets-Sheet 1 Original Filed Sept. 28.1951 v 22 28 2s Q 4 42- a rh M1 27 25 Z 1 2 I0 I FIG. 3

STEERING STEERINGOOLUMN l6"- coNNEc11m CY :7 I8 7 q l L MOTOR M1A FIG. 7

36 r 22 35 izgijlz w \\2\\ v1- lzo 121 as 37 I24 35 I5 I27 SOL zzvmvrox.

. WALTER FERRIS BY o 1/ M 40 39 129 ATTORNEY Dec. 18, 1956 W. F ERRISSTEERING CONTROL. FOR INDUSTRIAL TRUCK WITH HYDRAULIC WHEEL DRIVE MOTORSOriginal Filed Sept. 28. 1951 3 Sheets-Sheet 2 ENGINE VALVE V1 LI in UTO LIFT APPARATUS T\ VALVE V2 INVENTOR. WALT ER FERRIS WWW ATTORNEY Dec.18, 1956 w. FERRIS 2,774,434

STEERING CQNTROL FOR INDUSTRIAL TRUCK WITH HYDRAULIC WHEEL DRIVE MOTORSOriginal Filed Sept. 28, 1951 3 Sheets-Sheet 3 42 M1 FIG. 5

:43 m2 1 424 4: '36 FIG. 10

J I35 |4| i 34 -V 2 INVENTOR.

WALTER FERRIS ATTORNEY United States Patent and STEERING CONTROL FORINDUSTRIAL TRUCK WITH HYDRAULIC WHEEL DRIVE MOTORS Walter Ferris,Milwaukee, Wis assignor to The Oilgear Company, Milwaukee, Wis., acorporation of Wisconsin Original application September 28, 1951, SerialNo. 248,830. Divided and this application May 11, 1953, Serial No.354,233

13 (:laims. (Cl. 180-63) This application is a division of applicationSerial No. 248,830, filed September 28, 1951.

The invention relates to drives for automotive industrial trucks. Adrive constructed according to the invention is particularly adapted todrive an industrial truck of the type which will lift a load from anyheight within certain limits, move the load to a new location and placethe load at any height within those limits. Such trucks are well knownand in extensive use.

The present invention has as an object to provide 'a hydraulic drive forindustrial trucks.

Another object is to provide a truck drive which may be easily operatedand controlled.

Another object is to provide a truck drive having means for reducing theeffort required to steer the truck.

Other objects and advantages will appear from'the following descriptionof the truck drive shown schematically in the accompanying drawings inwhich the views are as follows:

Fig. 1 is a side view of one type of industrial truck to which theinvention may be applied.

Fig. 2 is a top plan view of the truck shown in Fig. 1 but with the rearwheels turned into position to enable the truck to make the sharpestpossible turn.

Fig. 3 is a view showing a part of the drive applied to the front wheelsof the truck and also showing a different arrangement of the rear wheelswhereby the truck may be turned about the center of the front axle.

Fig. 4 is a diagram of the hydraulic and electric circuits of a driveembodying the invention.

Fig. 5 is a view illustrating the displacement varying mechanism of oneof the hydraulic motors, the control mechanism shown being on the farside of the motor shown in the lower right hand portion of Fig. 4.

Fig. 6 is a view illustrating a different position of one of the valvesshown in Fig. 5.

Figs. 7 and 8 are views illustrating the functions of the selector valveshown in Fig. 4.

Figs. 9 and 10 are views illustrating the functions of each of the tworeversing valves shown in Fig. 4.

Fig. 11 illustrates another manner of operating one of the switchesshown in Fig. 4.

The truck shown in Figs. 1 and 2 includes a body 1 which carries theoperating and control mechanism, a vertical guide 2 which is supportedupon the front end of body 1, a slide 3 which is closely fitted in guide2 for vertical movement and a pair of forks 4 which are fixed to slide3.

Body 1 is supported by a pair of rubber tired front wheels 5 and 6 andby a pair of rubber tired rear wheels 7 and 8. Front wheels 5 and 6 areconnected to the driving mechanism of the truck and rotate upon oppositeends of a front axle 9 (Fig. 3) carried by the frame 10 of body 1. Eachof rear wheels 7 and 8 rotates upon a separate axle which is pivotallysupported by body 1. Steering of the truck is effected by turning asteering wheel 11 fixed to the upper end of a steering column 12 icewhich is connected to the rear wheels 7 and 8 by suitable steeringconnections not shown.

The arrangement is such that the truck may be advanced and steered todirect forks 4 beneath a load and then the forks may be raised to liftthe load. The truck may then be moved until the load is over a desiredlocation after which forks 4 may be lowered to deposit the load in thatlocation. Since such trucks are well known and in extensive use, furtherillustration and description of a conventional truck is deemedunnecessary.

When the rear wheels are mounted upon separate pivotally supported axlesand are turned as far as possible as indicated in Fig. 2, the truck willmake a right angle turn about a point which is on the axis of the frontwheels and is spaced some distance from the truck, as indicated at 13 inFig. 2. However, a truck may have'its rear wheels so arranged that thetruck will make a right angle turn about the center of its front axleand thereby require less space for turning.

As indicated in Fig. 3, the truck may be provided with a pair of rearwheels 7 and 8 which are arranged close together and are mounted upon anaxle 15 carried by a bearing block 16. The rear part of body 1 issupported from bearing block 16 by means of a support 17 which isconnected to steering column 12 by a suitable drive or steeringconnection 18. Support 17 is connected to frame 10 of body 1 and tohearing block 16 in such a manner that it may be rotated by drive 18 butcannot move in any other direction relatively to body 1 and rotation ofsupport 17 will cause rear wheels 7 and 8 to turn about the verticalaxis of support 17. Preferably, the connection between block 16 andsupport 17 is such that, when the truck is on or moving over an unevensurface, rear axle 15 may tilt in order to permit both rear wheels toremain in contact with that surface. It is also possible to mount thetwo rear wheels on separate axles as in the conventional truck shown inFig. 2, to support the two rear axles in such a manner that they may beturned parallel to the truck body and to connect the rear axles tosteering column 12 by steering connections through which the rear axlesmay be turned through an angle of 90 but the arrangement shown in Fig. 3is much simpler.

The particular arrangement for supporting body 1 upon the rear wheelshas not been illustrated nordescribed in detail because any suitableconstruction may be employed which will permit the rear wheels to turnabout the center of the rear axle so that, when the rear wheels areturned at right angles to the longitudinal 4 journaled in frame 10.Shaft 23 has a bevel gear 24 fixed thereon and in mesh with a bevelpinion 25 fixed upon-a shaft 26 which is journaled in frame 10 and isconnected by a coupling 27 to the shaft 28 of motor M1. The drive forwheel 6 is the same as the drive for wheel 5 and like parts have beenindicated by like reference numerals so that further description thereofis unnecessary.

As indicated in Fig. 4, liquid for energizing motors M1 and MlA issupplied by a variable displacement main pump P1 which is driven by aninternal combustion engine 30 as by means of a shaft 31. Liquid forcontrol purposes is supplied by a gear pump P2 which draws liquidthrough a channel 32 from a reservoir 33 and discharges liquid into abranched supply channel 34.

Gear pump P2 is driven in unison with pump P1 and is arranged within thecasing thereof accordingto common practice. The liquid discharged bygear pump .P2 in excess of requirements is exhausted into reservoir 33through a relief valve,(no t;shown) which. is. arranged within the pumpcasing accordingto theusual practice and which enables pump R2 tomaintain a constant low pressure in channel 34.

'Fpr the purpose of illustration, reservoir33v has. been shown separatefrom pump P1 but inpractice it tisreither arranged within. thecasing of,pump P1 or it, constitutes vba s p W ch-human ismo n ed, as istcustcm ytthatlsa a e mmnu p landlizimay drain rect- 3 info s vQir. 33- lquidfonmakius ptl' ak se los es as ppl d to r e atake f a mnBL- ther diretly; ifro s s iq n o b s ar Pump. 2.

mp A s a apted o i cha quidrthrous shan sl, 3 nd to ban; liquid r turn dto. i through a h lms z 6- Ch nne s 3. and: -latet o na t d t a ayd au ts lly snsra sdn n e ec ic i QntI 1 d l6ctor va v Y wh ch lsah sa aai Qtamlet a1 and t -a Pair o ,sh anfils and-%: emula d I he e Channels 37and 38 are adaptedtojirectliquid to an d f n.. h?. .1?i2 ra s f rassistin th Jitt n -mec n P hwhich appsr uah s n chollu trat sltnor smba, as t; auna earnes Q he reseut; i v n q Qant s-" d-a9 re h9fl5 I9twohyd aul qallsi r e and as i p tm lsd r versing-halve ZT n V 9 Pot tthe directi n 'Qf.; 1 .er.at n of ,rnotors M1 and MIA respectivelyvalveflfl isgcon es e o mo M1 byfi iq-shsme syfland: 4mm. valve.vzaisc'qmepted to motq; M1A- bytwo ,channels 41 iand4z I l /I c' to"rjsM1 and M1A preferably are of the yanetype andfmay' be similarto themotorshownin Patent.,No. 2,630,681 to which reference, may be had fordetails of construction. Since motorsMl and MIA are identical,

' a' description of one will sufifice for bcth.

' As indicated; in Fig 5, motor Nil-has its mfichanism arrangedwit'hina. casing 43 to which ichannels v land 4; are, connected, The mechanismof motor Bil-includes two identical displacement varying members; 454and: 45 which are a daptedlto'be adjusted, respectively, by two pistons46 and '47Qwhi'ch, areurgedoutward,respectively, by twosp'rin'gs48, and49 and are fitted,respectively, in two cylinde' rsi 5Q and151 which arefixed to oppqsite sides of casing 43, 'Meniber il and piston 46 are heldin 'firrn engagement with opposite ends of a spacer block 52 by abolt'Sfi, Likewise, member 45 and piston 47 areheld infirm enga'gementwith opposite endsof a spacerblocl; 54 by abolt 55. Springs 48 and 49normally hol d 'rnembers 44Yand. 45in such positions that motordisplacement .is maximum.

'Pistons'46 and 47, cylinders '50 and;51- and; springs 433 and 4 9,constitute hydraulic servo-motor means which when s'il plied withjrnotive liquid. willldecrease the, dis-. placementfofmotor'lvl l andwhen connected to exhaust will increase the :displacement of motor M1 aswill pr s nt b ts ain Operation of thej seryorrnotor means iscontrolledby a pilot lvalve V3 co'tnprisingba body 57 having an axialbore and a yalye SS fitt'edv therein. Y Valve body 57 has an annulargroove or port 59 formed inthe. Wall of its bore and connected by achannel 60 to both of cylinders 50 and 51. Valve 58 controls,communication. between port 59 and an exhaust channel '61 and betweenport 59 V and a branch of gear pump supply channel 34-.

The other internal mechanism of the rnotor has not been illustrate d asit is only necessaryto state that, when valvle 58 is shifted toward theright from the PQSition'shoWn, liquidwill flow from channel 34 .throughvalve body S'T-and channel 6010 cylinders 50 and 51 and cause pistonsfld and 47 to move members 44 and 45 radially inward to thereby decrease,the displacement of the motor and Whenvalve 58 is shifted toward thelelftgfromthetpositionshown, the pressure in cylinders 5D and 51 isreduced so that springs 43 and 49 can cause pistons 46 and 47 to movemembers 44 and 45 radially outward to increase the displacement of themotor, liquid being ejected by pistons 46 and 47 from cylinders 50 and51 through channel 66) and valve body 57 into exhaust channel 61.

The center piston on valve 58 has been shown as being of the same lengthas port 59 because the valve is shown on too small a scale to illustratethe usual construction. That is, the piston usually is made longer thanthe port and is provided at each of its ends with tapered grooves tothereby obtain more accurate regula; tion of the rate at which liquidcan flow through the port.

Valve :58 normally occupies a neutral position as .shown and it isoperated through a suitable follow-up mecha nism which, after the valvehas been shifted to "client movement of pistons 46 and 47, causes thevalve to be returned to its neutral position responSQto the ,moyement ofpistons '46- 'and 47. As shown, valve 58 ispiv; otally connected to oneend of .a floating lever 62 which is pivoted intermediate its ends upona pin 63arranged in one end ofacontrol rod 64. The other end yof=leyer62 is connected by a pin 65 to onearm of a bell-crank V lever, 66 whichlis pivoted upon a stat-ionary pin 6,7: 'I-Qhe other arm of lever 66 ispivoted to -one-end o.fa ;link 68; which is slidable in a guide 69andhas an equa-lizer 7Q pivoted to its otherend. Equalizer 70 is engagedby the free ends of two bell-cram; levers 71 and 7-2 which are pivoted,respectively, upon stationary pins '73 iand 74 andhave the other endsthereof pivot-ed to spacenblocks 52 and 54 respectively. All lostmotionin the follow-up mechanism. is taken out in any suitable 'manner such;as -by means ofa spring 75 which urges valve 58--toward the right inrespect .to Fig. 5.

The arrangement is suchthahflwhen controlrod 64 is moved toward theright in respect to Fig. 5, lever 1621MB; pivottupon pin 65-and willmove valve 58 toward the right from its neutral position. leaves itsneutral position liquid will flow to cylinders 50land 5.1andiwillimovetpistons 46- and 47 inward .to decrease motor, displacementas previously explained. Spacer blocks 52 and 54 will move inward withthe pistons andtwill 'cause levers 71 and.7 2 to pivot {upon pins '73and 74 and toraise efqualizerl70' and -1in k 68; which will cause lever66 to pivotuponpin 6,7 a nd move the upperend of lever 62 toward theright so that, as soon as movement ofco ntrolrod 6'4 ceases, lever 62will .pivot upon pin filandtreturn'valve 58 to its-neutral position. Thesum. of the -movements of. .pistons 50' and 51 and consequently.naval-anon in the displacement .of the motor, is thus proportional tothe distancethrou-gh whichtcontrol' rod 64;;Iis-inoved.

When control rod 64 is moved toward the left-12h? displacement varyingmechanism will Orieratesu-bstanti-aHy in the abovedescribednianneriexcept,thatmotor displace Inentwill beincreasedin'steadof reduced and each-part will move in a direction,'pposiite tothedirectionimwhich it moves when control rod 64' vis moved.towar d the right, spring 75 providing the force for holding equalizer,70. in cont-act-withtthe ends of; levers 71 and 72,, V

' Equalizer 70 is i pivoted. tot linlg '68.;insteadof being rigidlyconnected thereto for, the ;rea-son, that since, cylin; defs, 5.0., and51 ai'e connected in. parallel, there is 1 no assurance that both thepistons-4,6 and 47 one througheiactly the same distance but it is not hetl 1 a t .pi stons;46 andfi'leach move throughreiractl the earnerdistance as a given vania tion in motor displac si m ine h s m fthentances. hr gh hich the two pistons are moved. Each of pistonsfld'andis ipreventedifrom moving ,too farin eitherydir n by suitable stops (notshown) accordinggto the usual pra 7 cc Control rod 64 is connected by. acaged spr ing 7 6 to upon its other end and arranged in a cam track 7?formed in aLca'r'nwheel -wliich is connected by adrive ,81,-to steering.column 12 so that pilot valve V3 will be operated in response torotation of steering wheel 11 as presently be explained.

Cam wheel 80 is so connected by drive 81 to steering column 12 that itwill be rotated through an angle of 90 when steering wheel 11 is turnedfar enough to turn rear wheels 7 and 8 at right angles to front wheelsand 6.

Cam track 79 includes a long concentric portion 79 which extends throughan angular distance of a little more than 180, a very short concentricpart 79 which is diametrically opposite to and has the same radius aspart 79 and two parts 79 and 79 which curve inward from opposite ends ofpart 79 to points close to part 79* and then slope outward and join theends of part 79 In order that the displacement of motor M1 may bereduced to a predetermined and thereby cause the motor to operate athigh speed, an abutment 82 is fixed upon control rod 64 and engaged bythe stem of a piston 83 (Fig. 5) which is fitted in a stationarycylinder 84 and forms therewith a servo-motor 85. When servomotor 85 isenergized, it will move control rod 64 toward the right in respect toFig. 5 against the resistance of caged spring 76 to thereby cause thedisplacement of motor M1 to be reduced as explained above. Piston 83 andcylinder 84 are so proportioned and cylinder 84 is so located thatpiston 83 will stall against the end of cylinder 84 when it has movedcontrol rod 64 just far enough to cause the displacement of motor M1 tobe reduced to a predetermined minimum such as one-third of maximumdisplacement.

Liquid for energizing servo-motor 85 is supplied thereto under thecontrol of a valve V4 comprising a valve body 86 and a plunger 87 fittedin body 86 and having its stem connected to a lever 88. Servo-motor 85is connected by a channel 89 to body 86 at a point spaced from one endthereof. Supply channel 34 is connected to body 86 at a point spacedfrom channel 89 and an exhaust channel 90 is connected to body 86 ateach end thereof.

The arrangement is such that, when valve plunger 87 is shifted to theposition shown in Fig; 6, liquid will flow from supply channel 34through valve body 86 and channel 89 to cylinder 84 and cause piston '83to move abutment 82 and control rod 64 toward the right in respect toFig. 5, thereby reducing the displacement of motor 1 as previouslyexplained. When plunger 87 is returned to its neutral position as shownin Fig. 5, caged spring 76 will move abutment 82 and piston 83 towardthe left and piston 83 will eject liquid from cylinder 84 throughchannel 89 and valve body 86 into exhaust channel 90.

The control mechanism for motor MIA is the same as the control mechanismfor motor M1 except that it is arranged oppositely thereto, roller 78 onrod 77 be- .ing arranged in cam track 79 diametrically opposite roller7-8 and channel 89 being connected to a servomotor 85 Therefore, as tothe parts which appear in Fig. 4, like parts have been indicated by likereference numerals with the exponent a added to the reference numeralsapplied to the control for the motor MIA so that further descriptionthereof is unnecessary.

Main pump P1 may be of any suitable type but it has been indicated asbeing of the same type as motors M1 and M1A. That is, it has beenindicated as being a vane type pump having the same displacement varyingmechanism as the motors. Pump P1 may have its displacement reduced by aconstant force and increased by a controlled force according to theusual practice but, in order to simplify the drawing and thedescription, it has been shown as being provided with a control which isthe same as that shown in Fig. 5 except that the floating lever 62*,which corresponds to the lever 62 shown in Fig. 5 is connected to acontrol rod 95 instead of to a control rod 64., Therefore, as to theparts of the control which appear in Fig. 4, like parts havebeenindicated by like reference numerals with the exponent b" added tothe numerals applied to the control for pump P1 so that a description ofthe pump'control is unnecessary.

The displacement of pump P1 and the speed of engine 30 are regulated inresponse to operation of a foot pedal 96 which is pivoted to a support97 by means of a shaft 98. The mechanism for regulating pump P1 andengine 30 in response to operation of pedal 96'is quite complicated buthas been simplified in Fig. 4 for the purpose of illustration. At thispoint it should be emphasized that the drawings are schematic andillustrate the functions of the parts but d iller from the actualconstruction and location of the parts. As shown, foot pedal 96 has alever 99 formed integral therewith and connected by a link 100 to a camwheel 101 which is rotatably supported by a shaft 102. Camwheel 101 hasa cam track 103 formed therein at one side of shaft 102 and acam track104 formed upon its periphery at the other side of shaft 102. Cam track103 has arranged therein a roller 105 which is rotatably supported uponthe end of control rod 95. Cam track 104 is engaged by a roller 106carried by one end of a lever 107 which is pivoted intermediate its endsupon a stationary pin 108. The other end of lever 107 is pivoted to theouter end of a rod 109 which controls the flow of fuel to engine 30.Roller 106 is held in contact with cam track 104 by a spring 110 shownarranged between the block of engine 30 and an abutment 111 which isfixed upon control rod 109.

When cam Wheel 101 is in its neutral position as shown, the centers ofcam tracks 103 and 104 are on the horizontal centerline of cam wheel101, cam track 103 is holding pump P1 at zero displacement and cam track104 is holding engine 30 at idling speed. Cam tracks 103 and 104 aresymmetrical about the centers thereof so that the same adjustments ofengine 30 and pump P1 will be effected by rotation of cam wheel 101regardless of the direction of rotation. Preferably, cam tracks 103 and104 are so shaped that rotation of cam wheel 101 through a short angulardistance in either direction will cause engine 30 to be slightly speededup before the displacement of pump P1 is increased from zero and furtherrotation of cam wheel 101 will cause the speed of engine 30 and thedisplacement of pump P1 to be increased simultaneously.

Lever 99 on foot pedal 96 is urged downward by a spring 112 and isengaged by a plunger 113 fitted in a bore 114 formed in support 97.Plunger 113 is urged upward by a spring 115 which is strong enough toovercome the force exerted by spring 112. The upward movement of plunger113 is limited by nuts 116 which are threaded upon its stem and normallyengage the underside of support 97. The arrangement is such that plunger113 and springs 112 and 115 normally hold pedal 96 in a neutral positionas shown in full lines and indicated by the letter N.

Lever 99 has a switch actuator 117 on the free end theerof to operate amicro-switch S1 which controls operation of reversing valves V2 and V2.Switch S1 is so located that actuator 117 is in contact therewith whenpedal 96 is in its neutral position so that, as soon as pedal 96 startsto rotate in a clockwise direction in respect to Fig. 4, actuator 117will close switch S1. Actuator 117 is so shaped and of such length thatit will hold switch S1 closed when pedal 96 is rotated toward theposition shown in dotted lines and indicated by the letter R.

Selector valve V1 may be of any suitable construction and 'be operatedin any desired manner but for the purpose of illustration it has beenshown in Figs. 7 and 8 as including a body 120 having formed therein anaxial bore 121 with which channels 35, 36, 37, 38, 39 and 40communicate, a valve plunger 122 which is fitted in bore 121 to controlcommunication between the several channels and a spring 123 which isarranged in one end of bore .gear pumpP2 will discharge liquid throughits relief valve and maintain a low pressure in channel 34 and thedisplacement of pump P1 will be zero so that the truck is stationary.

If foot pedal 96 is then rotated in a counter-clockwise direction, lever99 and link 1430 will rotate cam wheel 101. Cam track 104 will moveroller 106 outward to increase the speed of engine 30 and cam track 103will move roller 105 and control rod 95 toward pump P1 which will causethe displacement of pump P1 to be increased from zero in the same mannerthat moving control rod 64 toward motor M1 causes the displacement ofmotor M1 to be increased as previously explained.

Pump P1 will then deliver liquid through channel 35, valve V1, channel39, valves V2 and V2*, and channels 41 and 41 to motors M1 and MIA andcause them to drive the truck forward. Further rotation of foot pedal 96will further increase the displacement of pump P1 and the speeds ofengine 30 and pump P1 until pedal 96 has been rotated into the positionshown in dotted lines and indicated by the letter F at which time engine30 is at full speed, pump P1 is at maximum displacement and the truck isbeing driven at the maximum speed within the low speed range.

If a' higher speed of the truck is desired, lever 88 may be, operated toshift the plunger 87 of valve V4 to the position shown in Fig. 6. Thenliquid will flow from supply channel 34 through valve V4 and channel 89to servomotors 85 and 85 and cause them to move control rods 64 and 64against the resistances of caged springs 76 and 76 and thereby reducethe displacements of motors Ml and M1A as previously explained. Then thespeed position as shown in Fig. 5 so that liquid can escape fromservomotors 85 and 85 and permit caged springs 76 and 7 6*- to returncontrol rods 64 and 64 totheir normal positions and thereby cause thedisplacements of motors M1 and MIA to be increased to maximum aspreviously explained.

- As the truck moves forward, it may be turned in one direction or theother by rotating steering wheel 11, thereby causing rotation of camwheel 80. Rollers 78 and '78 are arranged in cam track 79 diametricallyopposite each other and are in the end portions of concentric part 79when the rear wheels of the truck are parallel to the front wheelsthereof. Since concentric part 79* extends through slightly more than180 rollers 73 and 78 will not be moved radially of cam wheel 80 whensteering wheel 11 is turned slightly as the truck is steered along anearly straight path. But when steering wheel 11 is turned far enough ina direction to rotate cam wheel 80 through a substantial angle in acounterclockwise direction in respect to Fig. 4 to thereby turn thetruck through a substantial angle, roller 78 will enter cam track part79 which will cause roller 78 to pull rods 77 and 64 toward the centerof cam wheel 80 and thereby efiect a reduction in the displacement ofmotor M1 in the previously described manner. Roller 78 will remain inconcentric cam track part 79 so that the displacement of motor MIA isnot reduced.

Turning steering wheel 11 in counterclockwise direction will cause thetruck to turn in such a direction that front wheel 5, which is driven bymotor M1, is on the inside of the turn. Reducing the displacement ofmotor M1 reduces the torque exerted by motor M1 and enables motor MIA,which remains at full displacement, to exert upon outside wheel 6 atorque which is greater than the torque exerted upon inside wheel 5 bymotor M1. Applying to the outside wheel a greater torque than is appliedto the inside wheel assists the operator in steering the truck.

If it is then desired to opi When steering wheel 11 is turned far enoughto turn the rear wheels at right angles to the front wheels, cam wheelwill be rotated which will cause roller78 to be moved radially outwardinto concentric. cam track part 79 Roller 78 will move rods 77 and 64toward the right in respect to Fig. 4 which will cause the dis placementof motor M1 to be increased to maximum as previously explained. A

Just as or just before roller 78 passes from cam track part 79 into camtrack part 79 lever 151 of switch S3 is shifted in a direction to causecontact to connect contact 152 to contact 154. If switch S3 is arrangedas indicated in Fig. 4, lever 151 is operated by the operator. If switchS3 is arranged as indicated in Fig. 11, lever 151 is operatedautomatically by actuator 162 or it may be operated manually beforeactuator 162 engages lever 151. Connecting contact 152 to contact 154establishes a circuit to energize solenoid 144 which will cause theplunger 137 of valve V2 to assume the position shown in Fig. 10 aspreviously explained. With valve plunger 137 in the position shown inFig. 10, liquid will flow from channel 39 through valve V2 and channel42 to motor M1 which will thus be reversed and will drive front wheel 5in the opposite direction and thereby cause the truck to spin about thecenter of front axle 9.

The truck may be turned completely around or through any desired angle.When the truck has been turned far enough, steering wheel 11 and lever151 are returned to their normal position which will cause cam wheel 80to be returned to its normal position and solenoid 144 to be deenergizedand permit the parts of valve V2 to be returned to their normalpositions.

When steering wheel 11 is turned far enough in a direction to rotate camwheel 81 through a substantial angle in a clockwise direction from theposition shown in Fig. 4, the drive will operate in the above describedmanner but cam track portion 79 will move roller 78 toward the center ofcam wheel 34) to reduce the displacement of motor M1A and, if cam wheel84) is rotated through 90 from its normal position, roller 78 will bemoved outward as it passes from cam track part 79 into cam track part 79which will cause the displacement of motor M1A to be increased tomaximum and at the same time lever 151 of switch S3 is shifted, eithermanually or automatically to connect contact 153 to contact and therebyestablish a circuit to energize solenoid 144a which will cause valve V2to operate and reverse motor MlA.

When the parts are in the positions shown in Fig. 4. the track may bedriven rearwardly by rotating foot pedal 96 toward the position shown indotted lines and indicated by the letter R. As soon as pedal 96 startsto rotate, actuator 117 on lever 99 will close switch S1 which willestablish circuits to energize solenoids 144 and 144 thereby causing theplunger 137 of valves V2 and V2 to be shifted to the positions shown inFig. 10. Rotation of pedal 96 will cause pump P1 to discharge liquidthrough channel 35, valve V1 and channel 39 at the rate determined bythe angular distance through which pedal 96 is rotated from its neutralposition as previously explained. But with valves V2 and V2 shifted, theliquid discharged into channel 39 will flow through valves V2 and V2andchannels 42 and 42 into motors M1 and MIA and cause them to drive thetruck rearward.

The drive illustrated and described herein may be modified in variousways and adapted to various vehicles without departing from the scope ofthe invention which is hereby claimed as follows:

1. A drive for a vehicle having a body, a plurality of wheels forsupporting said body and including a pair of driving wheels, and meansfor steering said vehicle including a steering wheel; said drivecomprising two hydraulic motors each of which is connected to one ofsaid driving wheels and has means for varying its displacement, meansfor supplying motive liquid to both 11 l t ofsaid motors to enable thesame to rotate said driving wheels, a cam wheel having ,a cam; trackthereQl means for rotatinglsaidv cam wheel in response to rotation ofsaid steering wheel, control means for efiecting operation of; thedisplacement varying means of each of said motors and including anelement foradjusting said control, and a cam follower carried by each ofsaid elements and engaging said cam track to cause said elements toadjust said control means in response to rotationof said cam wheel; saidcam track being so shaped that during rotation of said cam Wheel ineither direction from a neutral position said track will hold theelement of the control meansfor one of said motors stationary and willmove the element of the control means for the others of said motors in adirection to cause that control means to efliect a reduction in thedisplacement of said other motor.

2. A drive according to claim 1 in which each ofsaid cam' followers isconnected to one of said elements by means including yieldable means andwhich includes two hydraulic servo motors formoving said elementsrespectively against the resistances of said yieldable means and eachhaving a limited stroke of such length that when energized saidservo-motorswill move both of said elements just far enough to causesaid control means to effect a reduction in the displacement of each ofsaid motors to a predetermined minimum, a source of pressure liquid; andmeans including 'a valve for connecting both of said servo-motorsto saidsource and to exhaust alternatively.

3. A drive for a vehicle having a body, aiplurality of wheels forsupporting said body and including a pair of driving wheels, and meansfor steering said vehicle including a steering wheel; said drivecomprising two hydraulic motors each of which is connected to one ofsaid driving wheels and has means for varying tis displacement, meansfor supplying motive liquid to both of said motors to enable the same torotate said driving wheels, a cam wheel having a cam track thereon,means for rotating said cam wheel in response to rotation of saidsteering wheel, follow-up control means for effecting operation of thedisplacement varying means of each of said motors, two control rods eachof which is-connected at one of its ends to one of said control means,and two cam followers carried by the other ends of said rodsrespectively and engaging said cam track at points diametricallyopposite each other; said cam track being so shaped that during rotationof said cam wheel in either direction from a neutral position said trackwill hold the rod of the control means for one of said motors stationaryand will move the rod of the controlmeans for the other of said motorsin a direction to cause that control means to effect a reduction in thedisplacement of said other motor.

4. A drive accordingto claim? in which each of said control rodsincludesa first part having one end thereof connected to one of saidcontrol means, a second part having one of said earn followers onone endthereof and yieldable means connecting the other ends of said parts toeach other, and which includes-two hydraulic servo-motors for movingsaid first parts respectively against the resistance of said yieldablemeans and'each having a limited stroke of such length-that whenenergized said servo-motors will move both of said first'parts just farenough to cause said control means to effect a reduction in thedisplacement of each of-said motors to r a predetermined minimum, asource of pressure-liquid, and means including a valve forconnecting-both of-said servo-motors to said source-and toexhaustalternatively.

5. A drive for a vehiclehavinga body, a pair-of driving wheels rotatableupon an axis which is s'tationary in respect to said body, atleast-one-other wheel rotatable upon anaxis which may be turned throughan angle of at least 90 in'respect to the axis of said driving wheelsand means including a steeringwheel for turning the axis ofsaidotherwheel-intres pect to theaxis of said t V 12 7 driving wheel tothereby steer said vehicle, said drive 'coin-' prising two hydraulicmotors each of whichis connected to one of said driving wheels and hasmeans for'varying' its displacement, means including a p umpforsupplying motive liquid to's'aidmotors to enable the same to rotatesaid driving wheels, means for connecting said-pump to said motors, a mmwheel having a cam track'fthereon, means responsive to rotation of saidsteering wheel for To-' tating-said cam wheel through an angulardistance equal to the angle through which the axis of said other wheelis turned in response to rotation of said steering wheel,

control means for effecting operation of the displacement varying meansofeach of said motors and includ: ing an element for adjusting saidcontrol, and a cam follower carried by each of said elements'and-enga-ging; said cam track to cause said elements to adjustsaid-controlmeans in response to rotatioriofsaid cam wheel; said cam wheel being ina neutral position when said other wheel is parallel or nearly parallelto said driving wheels and said cam track being so shaped: that it willhol'diboth of said elements stationary in such positions. as to causesaid control means to maintain thedisplacements of said motors atmaximum when said cam wheel is in said neutral position, it will holdthe elementof the control means for one of said motors in saidstationary position during rotation of said. cam-Mwheel in.either-direction from its neutral position, it will move the elementuofthe control means for the other of said motors in adirec- I in thedisplacement of said other motor to maximum.

6. A drive according to claim 5 in which; eachv ofsaid cam followers isconnectedqto one of. said elements: by means including yieldable, means,and; which includes two hydraulic servomotors for moving. said elementsrespectively against theresistancesof said-.yielda-ble means and eachhaving a limited stroke of such length thatrWhen energized saidservomotors WilllIlOVQ'bQihg'Of, saidgelements just far enough ,tocausesaid control meansto-efict a reduction in the displacement of'eachof; said motors to a predetermined minimum, a source of-pres sureliqurid, and, means including a valve forconnectingboth Qf: saidservomotors to said sourceand. to exhaustalternatively.

7. A drive for a vehiclehaving -a;,body,.;a.plurality f l f uppor i g ah dyan --inc.1ud g:-a;pai.r of driving, wheels, and meansforsteeriug'said vehicle including asteeringwheelysaid drive cpmp 'isilg-twovariable displacement hydrau-l=ic; motors; each-of which ;is-,connected toone of said driving wheels, means; for supplying motiveliquid to both of said motors 'to enabl -thehaving one end thereofpivoted tosaid' pilot -v-alve, a follow-up linkage connecting theother-.endo'fsaidlever to said servomotormeans, and a control rodhavingoneof its-ends pivoted to said lever-intermediatethe ;endst thereof andits other end provided with a cam follower which engages said cam trackso that rotation of said cam wheel will cause said rod to swing saidlever upon said linkage and shift said pilot valve from its neutralposition to thereby effect operation of said servo-motor means andoperation of said servomotor means will cause said linkage to swing saidlever upon said control rod and return said pilot valve to its neutralposition.

8. A drive according to claim 7 in which said control rod includes afirst part having one of its ends connected to said floating lever, asecond part having said cam follower on one of its ends and yieldablemeans connecting the other ends of said parts to each other, and whichincludes a hydraulic servomotor for moving said first part against theresistance of said yieldable means in a direction to efiect a reductionin motor displacement and having a limited stroke of such length thatwhen energized said servomotor will move said first part just far enoughto ettect a reduction in motor displacement to a predetermined minimum,and means including a valve for connecting said servomotor to saidsource and to exhaust alternatively.

9. A drive according to claim in which said means for connecting saidpump to said motors includes a reversing valve connected between each ofsaid motors and said pump, and which includes means for shifting each ofsaid valves to thereby reverse the motor to which that valve isconnected, and means responsive to rotation of said cam wheel in eitherdirection to a position approximately 90 from its neutral position foreffecting operation of one or the other of said valve shifting means.

10. In a hydraulic drive, the combination of a hydraulic motor forconnection to an element to drive the same and having means for varyingits displacement, means connected to said motor for supplying motiveliquid thereto to enable it to drive said element, a control connectedto said displacement varying means for effecting operation thereof andhaving a member connected thereto, means for adjusting said member toselected positions, means connecting said adjusting means to said memberand including a caged spring, a hydraulic servomotor engaging saidmember for moving the same against the resistance of said spring andhaving a limited stroke of such a length that when energized saidservomotor will move said member just far enough to cause said controlto effect a reduction in the displacement of said motor to apredetermined minimum, a source of pressure liquid, and a valveconnected to said source and to said servomotor and operable to connectsaid servomotor to said source and to exhaust alternatively.

11. A drive for a vehicle having a plurality of wheels, said drivecomprising hydraulic motor means for driving said vehicle connected toat least one of said wheels and having means for varying itsdisplacement, means connected to said motor means for supplying motiveliquid thereto to enable the same to rotate said wheel, followup controlmeans for efiecting operation of said displacement varying meansconnected thereto, at least one control rod connected to said controlmeans for operating the same and including a first part and a secondpart and yieldable means connecting said parts to each other, meansconnected to said second part for moving it into and holding it inselected positions, a hydraulic servomotor engaging said first part formoving the same against the resistance of said yieldable means andhaving a limited stroke of such a length that when energized saidservomotor will move said first part just far enough to cause saidcontrol means to efiect a reduction in the displacement of said motormeans to a predetermined minimum, a source of pressure liquid, and avalve connected to said servomotor and said source and operable toconnect said servomotor to said source and to exhaust alternatively.

12. A drive for a vehicle having a pair of driving wheels, said drivecomprising a hydraulic motor connected to each of said wheels and havingmeans for varying its displacement, means connected to both of saidmotors for supplying motive liquid thereto to enable the same to rotatesaid wheels, control means for efiecting operation of the displacementvarying means of each of said motors connected thereto and including anelement for adjusting said control, a device for moving said elementsinto adjusted positions, a linkage including yieldable means forconnecting each of said elements to said device, two hydraulicservomotors engaging said elements respectively for moving the sameagainst the resistances of said yieldable means and each having alimited stroke of such length that when energized said servomotors willmove both of said elements just far enough to cause said control meansto efiect a reduction in the displacement of each of said motors to apredetermined minimum, a source of pressure liquid, and a valveconnected to said servomotors and said source and operable to connectboth of said servomotors to said source and to exhaust alternatively.

13. A drive for a vehicle having a pair of driving wheels, said drivecomprising a hydraulic motor connected to each of said wheels and havingmeans for varying its displacement, means connected to both of saidmotors for supplying motive liquid thereto to enable the same to rotatesaid wheels, follow-up control means connected to the displacementvarying means of each of said motors for effecting operation thereof, acontrol rod connected to each of said control means for operating thesame and including a first part and a second part and yieldable meansconnecting said parts to each other, a device connected to said secondparts for moving the same into selected positions, two hydraulicservomotors engaging said first parts respectively for moving the sameagainst the resistances of said yieldable means and each having alimited stroke of such length that when energized said servomotors willmove both of said first parts just far enough to cause said controlmeans to effect a reduction in the displacement of each of said motorsto a predetermined minimum, a source of pressure liquid, and a valveconnected to said servomotors and said source and operable to connectboth of said servomotors to said source and to exhaust alternatively.

References Cited in the file of this patent UNITED STATES PATENTS901,055 Allen Oct. 13, 1908 2,161,439 Thoma June 6, 1939 2,177,097 Doeet al. Oct. 24, 1939 2,246,018 Snyder June 17, 1941 2,320,727 Herman eta1 June 1, 1943 2,393,324 Joy Jan. 22, 1946 2,478,481 Griflith Aug. 9,1949 2,516,662 Vickers et al July 25, 1950 2,547,578 Holmes Apr. 3, 19512,588,866 Moon Mar. 11, 1952 2,598,538 Haynes May 27, 1952

